In a previous post I got to a compiling and linking build for the STM32L Discovery board, but it didn’t actually print anything. Turns out I’d made one of the classically common mistakes with STM32 development, and one of the weakpoints in libopencm3’s api for the RCC module.

rcc_peripheral_enable_clock(&RCC_APB1ENR, RCC_APB2ENR_USART1EN);

The API unfortunately needs both the register, and the bit, and if you can’t see the problem, don’t worry, you’re not alone. The problem is that I was turning on a feature in APB1 (ONE) with a bit definition designed for APB2 (TWO)

When I actually turned on the USART peripheral, everything started working as I expected. I can’t believe how often I’ve done something like this. Or how often I’ve simply not turned on what I needed. Later, I added code to support USART2 and USART3, but…. didn’t turn on those peripherals. Silly me.

But, that does mean that my Contiki port to the STM32L Discovery board is alive: https://github.com/karlp/contiki-outoftree

Much more to come! Radio drivers and more examples and onwards!